RU2672877C2 - Method for producing butadiene and hydrogen from ethanol in two reaction steps with low water and power consumption - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: invention relates to a method for producing butadiene from ethanol feedstock containing at least 80 wt% ethanol, comprising at least step A) conversion of ethanol to acetaldehyde, step B) conversion of an ethanol/acetaldehyde mixture to butadiene, step C1) treatment of hydrogen, step D1) extraction of butadiene, step D2) first purification of butadiene, step D3) further purification of butadiene, step E1) treatment of output streams, step E2) removal of impurities and brown oils and stage F) washing with water.EFFECT: disclosed method allows to increase productivity and reduce emissions.15 cl, 2 ex, 7 dwg

Description

FIELD OF THE INVENTION

The invention relates to a method for producing butadiene from ethanol, carried out in two reaction stages: the first reaction stage, which produces acetaldehyde, and the second stage, which produces butadiene from a mixture of ethanol and acetaldehyde.

State of the art

Methods for producing butadiene from ethanol were developed, in particular, by Russians based on the work of Lebedev in the 20s (method in the 1st reaction stage) and by Americans during the Second World War, based on the works of Ostromyslensky (method in the 2nd reaction stage: dehydrogenation of ethanol in acetaldehyde, then the production of butadiene from ethanol / acetaldehyde). This last method, giving slightly higher outputs, was operated in the 40s in the United States. All installations of this type have long been stopped, mainly for economic reasons.

The method in the Lebedev or Ostromyslensky version has a conversion in one pass much lower than 50%, which entails significant re-treatment, and is complicated by the fact that it is necessary to accurately establish the ethanol / acetaldehyde ratio at the inlet to the second reactor.

The second problem of this method is the formation of a wide range of impurities of all kinds: saturated, unsaturated and aromatic hydrocarbons, as well as oxygen-containing products (such as alcohols, phenols, aldehydes, ketones, acids, esters, ethers, acetals).

Some of these by-products, both gaseous and liquid, under normal conditions of temperature and pressure, are formed in significant quantities. Of the gaseous by-products, hydrogen, carbon monoxide, carbon dioxide, C ₁ -C ₄ alkanes and olefins, and methyl ethyl ether can be mentioned. Of the liquid by-products, pentenes, pentadienes, diethyl ether, ethyl vinyl ether, hexenes, hexadiene, butanal, crotonic aldehyde, ethyl acetate, diethylacetal, butanol, hexanol, acetic acid can be mentioned. These gaseous and liquid by-products create problems for producing butadiene that meets the specifications, and also because their return to the reaction stages with ethanol and acetaldehyde leads to a decrease in the overall productivity of the installation. Their removal greatly complicates the separation process.

Other by-products are formed in small quantities. Hereinafter, “brown oils” will be referred to as all thousands of hydrocarbon and oxygen-containing compounds formed in reaction sections in which the boiling points are in the range from the boiling point of ethanol to 600 ° C. A feature of these brown oils is that they dissolve in ethanol but do not dissolve in water. Wherever they are diluted with a large excess of ethanol, they can contaminate and clog equipment. In addition, these brown oils lead to problems in the distillation column separating the water obtained from the reaction and unreacted ethanol. Indeed, brown oils are soluble in the water-ethanol stream supplied to the specified distillation column, but not soluble in the residue, consisting mainly of water. Therefore, the phase separation occurring in this column significantly reduces the separation efficiency. Brown oils are difficult to remove from the process because they consist of thousands of compounds having very different physicochemical properties. Therefore, some of these brown oils accumulate in the process, leading to a decrease in its effectiveness after several days, at best weeks of operation, and requiring periodic cleaning of certain streams. The resulting loss of ethanol and acetaldehyde reduces the overall productivity of the process due to costs that would currently be unacceptable.

Due to the numerous impurities generated in the process, the purification of butadiene is difficult. It entails the use of a combination of a large number of individual operations, such as washing, simple and extractive distillation. In the prior art, the use of extractive distillation using a solvent of bis (2-chloroethyl) ether (chlororex), which is currently prohibited due to its strong toxicity, is recommended. It is important to note that the specifications for butadiene are currently very stringent, due to the sensitivity of the butadiene polymerization catalysts. Thus, the reproduction of the sequence of individual operations according to the prior art does not allow to achieve modern specifications. For example, the specification for acetaldehyde in butadiene decreased from 1000 ppm to the current less than 10 ppm.

Synthetic rubber, chapter 4 (W.J. Toussaint, J. Lee Marah) provides an overview of the process developed by Carbide and Carbon, the main steps of which are briefly described below.

In the first reaction step, ethanol leaving the effluent treatment step is converted to a stream of ethanol / acetaldehyde mixture (hereinafter, ethanol / acetaldehyde stream). This step also gives a gaseous stream of hydrogen. Then, the ethanol / acetaldehyde stream is treated at the stage of processing the effluent, and it can be preliminarily sent to the butadiene extraction stage to isolate the ethanol stream and the acetaldehyde stream. The ethanol / acetaldehyde stream contains a significant amount of acetaldehyde (about 20 wt.%), Which is much more volatile than ethanol, and therefore more easily entrained in the gaseous stream.

The hydrogen stream is treated at the stage of washing with water, which allows you to select ethanol and acetaldehyde, carried away with hydrogen. An effective flushing to prevent a decrease in the overall plant productivity due to the loss of ethanol and acetaldehyde requires the use of at least 2 tons of water per ton of butadiene produced or, equivalently, about 5 tons of water per ton of acetaldehyde and ethanol released. Then the wash water needs to be cleaned at the stage of processing the effluent. Thus, the recovery of trace amounts of ethanol and acetaldehyde entails a corresponding increase in equipment size and energy consumption in the process. Hydrogen has a purity of the order of 99 mol%, or 90 wt.%.

Ethanol and acetaldehyde are fed to the second reaction step for converting the ethanol / acetaldehyde to butadiene mixture from the effluent treatment step. A liquid stream and a gaseous stream are obtained. Separation of products leaving the first reaction stage at the stage of processing the effluent to mix them again at the entrance to the second reaction stage leads to an increase in the size of the equipment and energy consumption in the process.

According to the prior art, the gaseous stream leaving the second reaction stage is washed with ethanol-rich but untreated streams, which results in the need to oversize the installation of the butadiene extraction stage and the processing stage of gaseous by-products and, therefore, the stage of processing the effluent.

The streams leaving the second reaction stage are treated in the butadiene extraction stage, to which a part of the ethanol / acetaldehyde stream from the first reaction stage is also fed. This step comprises at least one gas-liquid washing section and a rectification section. In the extraction step, a crude butadiene stream, a gaseous product stream, and a mixture of ethanol, acetaldehyde and water (hereinafter, ethanol / acetaldehyde / water stream) are obtained. The last stream can be returned to the head of the gas-liquid washing section of this stage. However, this return causes problems since the presence of water in ethanol reduces the solubility of butadiene. Therefore, in order to compensate for the decrease in solubility, it is necessary to increase the flow rate of the liquid to isolate the same amount of butadiene from the washed gaseous stream.

The crude butadiene stream is washed with water in the first purification step, then purified in the last purification, among other things, by extractive distillation using a bis (2-chloroethyl) ether (chlororex) type solvent. The water from the washing of the crude butadiene is treated at the stage of processing the effluent, and the impurities obtained in the last purification are removed from the process.

The first purification of butadiene allows the removal of acetaldehyde present in the crude butadiene stream leaving the butadiene extraction step. However, given the change in the specifications for carbonyl in butadiene between the 60s and today, the flow rate of water supplied to the stage of the first purification of butadiene must be greatly increased in order to reach the current specifications. Since the formed waste water stream is sent to the stage of processing the effluent, achieving specifications will lead to a significant increase in the size of the equipment and to an increase in energy consumption. In addition, increasing the flow rate of the wash water to achieve specifications is also expressed in the problems of separation of the butadiene / water mixture in the wash column.

The treatment step of the effluent streams allows the acetaldehyde stream, ethanol stream, water stream, liquid by-product stream and possibly brown oil stream to be separated from the various treated streams. This stage usually contains two to three distillation columns. The ethanol feed for the process is fed to the stage of processing the effluent at the level of ethanol / water distillation.

The brown oil stream, possibly obtained at this stage, is either removed from the process or processed at a special stage of processing liquid by-products and brown oils, which allows to obtain various streams suitable for reuse, such as a stream rich in ethyl acetate, or a stream rich in hexadiene, and minimize loss of ethanol and acetaldehyde with liquid by-products and brown oils.

The complexity of the recirculation between the various individual operations of the effluent processing step complicates the implementation of this step. In addition, phase separation that occurs in the columns creates problems for the process, in particular due to brown oils, and also due to the size of the equipment.

Gaseous by-products are treated in the gaseous by-product treatment step, where they are washed with a stream of water, which is then treated in the treatment step of the effluent.

US 1,977,750 describes the steps for converting ethanol to acetaldehyde and treating hydrogen. Ethanol partially reacts in the catalytic section. The effluent, consisting mainly of ethanol, acetaldehyde and hydrogen, is cooled before washing with water in a water-cooled condenser, then in a condenser into which a saline solution is supplied. All liquid effluents collected in these three separate operations are combined and distilled to recover acetaldehyde and unreacted ethanol.

US 2,249,847 describes the steps for converting ethanol to acetaldehyde and treating the effluents for the case where only acetaldehyde and its by-products are formed in the process. In particular, the benefits of introducing ethanol feed to the ethanol / water distillation column collection column at the stage of processing the effluent are described, this technique is reproduced in all later documents.

US 2,403,741 describes the steps for converting ethanol to acetaldehyde, converting ethanol / acetaldehyde to butadiene, treating hydrogen, extracting butadiene, first purifying butadiene and treating the effluent. The benefit of using the ethanol / acetaldehyde stream leaving the first reaction stage to carry out the extraction step of butadiene contained in the steam stream leaving the second reaction stage is described.

US 2,403,742 describes the steps for converting ethanol to acetaldehyde, converting ethanol / acetaldehyde to butadiene, treating hydrogen, extracting butadiene, first purifying butadiene and treating the effluent. The difficulty of returning the acetaldehyde stream leaving the processing stage of the exit streams to the second reaction stage is described, in particular, due to the presence of diethyl ether, which forms an azeotrope with acetaldehyde. Therefore, the stage of processing the effluent is carried out in a distillation column intermediate between the column producing acetaldehyde and the column producing ethanol to remove liquid by-products. This technique is found in all subsequent documents.

Patents US 2,403,743, US 2,393,381 and 2,395,057 describe various configurations of the effluent treatment step and the possible presence of a treatment step of liquid by-products and brown oils to minimize losses of ethanol and acetaldehyde. These documents teach that without the implementation of the described inventions, the purity of the acetaldehyde stream leaving the processing stage of the leaving streams can drop below 50 wt.%, Which leads to serious problems when it is returned to the second reaction stage. The proposed invention allows to obtain a stream of acetaldehyde / ethanol, leaving the stage of processing the effluent, with a purity higher than 80 wt.%, And in the best case, equal to 93 wt.%. However, the described separation units are obviously difficult to operate and require a lot of energy, taking into account the multiple recycling between different individual operations.

US Pat. No. 2,409,250 (Carbide and Carbon, 1944) describes sequential steps for the purification of butadiene (extraction, first purification and last purification of butadiene by super-fractionation). Get butadiene with a purity of 98.7%, but at the cost of a significant reduction in yield. To reduce these losses, products are selected on top of the super-fractionated butadiene purification columns and partially returned to the butadiene extraction step. This significant recirculation, in particular the return of the butene / butadiene stream to remove non-condensable gases, leads to oversized equipment.

Koppers, in US Pat. No. 2,439,587, offers an improvement in the Carbide and Carbon process by recovering a by-product of ethyl acetate and returning it to the second reaction step. Separation operations are complex and difficult to manage, since they use, among other things, side extraction, decantation, purging, washing with water, and lead to significant losses of ethanol and acetaldehyde.

US patent 1,948,777 (Carbide and Carbon, 1931) describes in detail the stage of the last purification of butadiene by extractive distillation using various solvents, including chlorex. While limiting the loss of butadiene in the head of the column, i.e. when the concentration of butadiene in the distillate is 0.2%, the purity of the butadiene obtained from below will be only 70%, whereas if you want to get pure butadiene below, that is 99%, the loss of butadiene in the head of the column will be too significant, with the concentration of butadiene in distill 30%. Thus, obtaining high-purity butadiene is achieved due to the low overall productivity of the installation.

The overall performance of the prior art circuits is low because the acetaldehyde stream returned to the second reaction stage is dirty, and given the loss of ethanol and acetaldehyde.

Although oil is currently the main source of butadiene, depletion of deposits in the future will lead to a complete rethinking of the old method to ensure the production of butadiene from alternative sources.

The object and purpose of the invention

The object of the invention is a method for producing butadiene from ethanol raw materials containing at least 80 wt.% Ethanol, including at least:

A) a step for converting ethanol to acetaldehyde containing at least one reaction section, to which at least a portion of the ethanol-enriched stream leaving step E1) is supplied, operating at a pressure of 0.1 to 1.0 MPa and a temperature of 200 ° C to 500 ° C in the presence of a catalyst, and a separation section, allowing to separate the stream leaving the specified reaction section, at least a stream of hydrogen in gaseous form and a stream of ethanol / acetaldehyde in liquid form;

B) a step for converting to butadiene containing at least one reaction section to which at least a portion of said ethanol / acetaldehyde stream leaving step A) is fed, a liquid stream enriched in ethanol leaving step C1), a portion of the stream enriched acetaldehyde leaving step E1), and wherein said section operates in the presence of a catalyst at a temperature of from 300 ° C to 400 ° C and a pressure of from 0.1 to 1.0 MPa, the feed rates being regulated so that the ethanol / mol ratio acetaldehyde inlet decree the reaction section ranged from 1 to 5; and also contains a separation section that allows you to split the stream leaving the specified reaction section into at least one gaseous stream and at least one liquid stream;

C1) a hydrogen treatment step comprising at least a compression section compressing said hydrogen stream leaving step A) to a pressure of from 0.1 to 1.0 MPa, and a gas-liquid washing section, to which it is supplied at a temperature of from 15 ° C to -30 ° C a portion of said ethanol stream from step E1) and a portion of said ethanol / acetaldehyde stream from step A), and also said compressed hydrogen stream is fed at a temperature of 25 ° C to 60 ° C, and at least one ethanol-enriched liquid stream and a purified hydrogen stream;

D1) a butadiene extraction step comprising at least a compression section compressing said gaseous stream exiting from step B) to a pressure in the range of 0.1 to 1.0 MPa, a gas-liquid washing section containing a washing column onto which an ethanol stream consisting of the indicated ethanol feedstock and / or a part of the ethanol stream exiting from step E1) is supplied from above at a temperature of 20 ° C to -20 ° C, and said gaseous stream exiting from step B) and cooled , and a distillation section operating at from 0.1 to 1 MPa, to which at least a liquid stream is supplied from the indicated stage B) and a liquid stream from the indicated gas-liquid washing section, wherein at the indicated stage D1) at least a gaseous by-product stream is obtained, the crude stream butadiene and ethanol / acetaldehyde / water stream;

D2) a first butadiene purification step comprising at least a gas-liquid washing section to which a crude butadiene stream exiting from step D1) is supplied from below and a water stream, which may be a water stream external to the butadiene production process, from above , and / or a part of the water stream leaving stage E1), wherein in the indicated washing section a pre-purified stream of butadiene is obtained from above, and a stream of spent water from below;

D3) a step for further purification of butadiene to which at least said previously purified butadiene stream exiting from said step D2) is fed, and at least a purified butadiene stream is obtained;

E1) an effluent treatment step to which at least water / ethanol / acetaldehyde raffinate exiting from step E2) is fed, and at least an ethanol enriched stream, an acetaldehyde enriched stream, and a water enriched stream are obtained;

E2) a step for removing impurities and brown oils, to which at least an ethanol / acetaldehyde / water stream exiting from stage D1) is supplied, and a water-enriched stream exiting from E1), and at least water / ethanol / acetaldehyde raffinate is obtained a stream of light brown oils and a stream of heavy brown oils;

F) a water washing step to which a gaseous by-product stream leaving step D1) is supplied, as well as a portion of the water enriched stream leaving from said step E1), and in which at least one water-alcohol mixture stream is obtained.

The authors of the application have established a diagram of individual operations that can mitigate the numerous disadvantages of the prior art. In particular, the separate operation scheme proposed by the invention eliminates gaseous impurities, liquid impurities and brown oils, while minimizing the loss of ethanol and acetaldehyde, thereby improving the overall performance of the unit while reducing the total water flow required for the separation stages, and obtaining very pure butadiene . A significant reduction in total water flow can reduce the energy consumption in the process and the size of the separation equipment.

DETAILED DESCRIPTION OF THE INVENTION

Raw materials

The ethanol feed used in the method according to the invention can come from any source, fossil, vegetable or animal, and, in particular, from processes for producing ethanol from plant sources. The specified feed contains at least 80 wt.% Ethanol, preferably at least 90 wt.% And preferably at least 93 wt.%. Very preferably, said ethanol feed meets the specifications of EN 15376 for ethanol for fuel.

Step A) Conversion of Ethanol to Acetaldehyde

According to the invention, step A) of converting ethanol to acetaldehyde comprises at least one reaction section to which at least a portion of the ethanol-rich stream exiting from step E1) is supplied, said portion preferably comprising at least 10% of the flow rate of said ethanol-rich stream from step E1), and to which at least a portion of said ethanol feedstock is optionally preferentially fed, and a separation section allowing separation of the stream from said reaction section at least the hydrogen stream in gaseous form and the ethanol / acetaldehyde stream in liquid form.

Said reaction section allows the conversion of ethanol to acetaldehyde in the presence of a catalyst, preferably consisting of a mixture of chromium oxide and copper oxide, or any other suitable catalyst. These catalysts are well known in the art.

The specified reaction section operates at a pressure in the range from 0.1 to 1.0 MPa, preferably from 0.1 to 0.5 MPa, preferably from 0.1 to 0.3 MPa, and at a temperature in the range from 200 ° C to 500 ° C, preferably from 250 ° C to 300 ° C.

Preferably, the degree of ethanol conversion is from 30% to 40% with acetaldehyde selectivity from 85% to 100%, preferably from 90% to 95%. The stream from said reaction section also contains by-products, such as crotonic aldehyde, butyraldehyde, diethyl acetal, ethyl acetate and acetic acid.

In said separation section, gas-liquid separation means known to those skilled in the art are used. It is preferable to use a gas and liquid separation unit operating at a pressure of 0.1 to 0.3 MPa and a temperature of 25 ° C to 60 ° C.

Step B) Converting Ethanol / Acetaldehyde to Butadiene

According to the invention, the step B) of converting to butadiene comprises at least one reaction section to which at least a part of said ethanol / acetaldehyde stream leaving from stage A) is fed, a liquid stream enriched in ethanol leaving from stage C1), a part of the stream enriched in acetaldehyde exiting from step E1), and preferably and optionally an ethanol-enriched stream from step E1) is supplied, and a separation section allowing the stream from said reaction section to be divided into at least one gaseous stream and at least one liquid stream. An external stream of acetaldehyde can also be fed to said reaction section.

The velocities of the various streams supplied to the reaction section of said step B) are selected so that the molar ratio of ethanol to acetaldehyde at the inlet of said reaction section is from 1 to 5, preferably from 1 to 3.5, more preferably from 2 to 3 and very preferably from 2.4 to 2.7.

The specified reaction section allows you to convert part of the mixture of ethanol / acetaldehyde in at least butadiene. The conversion selectivity of the ethanol / acetaldehyde mixture is preferably greater than 60%, preferably higher than 70%, very preferably higher than 80%. By selectivity is meant the molar ratio of the amount of butadiene in the stream from the specified reaction section to the amount of ethanol and acetaldehyde consumed in the specified reaction section. The degree of conversion of the ethanol / acetaldehyde mixture is preferably greater than 30%, preferably higher than 40%, preferably higher than 47%. By the degree of conversion is meant the molar ratio of the amount of ethanol and acetaldehyde in the stream from the specified reaction section to the amount of ethanol and acetaldehyde in the feed to the specified reaction section. The section operates in the presence of a catalyst, preferably a catalyst on a silica support selected from the group of catalysts containing tantalum, zirconium or niobium oxide, preferably containing 2% tantalum oxide (see, for example, Corson, Jones, Welling, Hincbley, Stahly, Ind. Eng Chem. 1950, 42, 2, 359-373). The specified reaction section operates at a temperature in the range from 300 ° C to 400 ° C, preferably from 320 ° C to 370 ° C and a pressure of from 0.1 to 1.0 MPa, preferably from 0.1 to 0.5 MPa, preferably from 0.1 to 0.3 MPa.

Preferably, about 65-80% of acetaldehyde is reacted in said reaction section. Thus, the stream from the specified reaction section still contains ethanol. Numerous impurities can form with butadiene, including ethylene, propylene, diethyl ether (DEE), ethyl acetate, butanol, hexanol, butenes, pentenes, pentadienes, hexenes and hexadiene.

Since the acetaldehyde stream leaving the effluent treatment step E1) is supplied to the indicated reaction section, the ratio of ethanol to acetaldehyde at the inlet of this section is adjusted by adjusting the proportion of the ethanol flow from the specified step E1) supplied to step A), and acetaldehyde is obtained. Indeed, the remaining part of the ethanol-enriched stream from the indicated stage E1) is supplied to the hydrogen treatment step C1) and forms, after washing the hydrogen stream, the indicated ethanol-enriched liquid stream exiting from the indicated step C1) and supplied to the indicated step B). However, this ethanol-rich liquid stream from step C1) contains very little acetaldehyde. Thus, thanks to the method of the invention, monitoring the ratio of ethanol to acetaldehyde at the inlet of said reaction section is facilitated.

In said separation section, gas-liquid separation means known to those skilled in the art are used. It is preferable to use a gas and liquid separation unit operating at a pressure of 0.1 to 0.3 MPa and a temperature of 25 ° C to 60 ° C.

Step C1) Hydrogen Treatment

According to the invention, the hydrogen treatment step C1) comprises at least one compression section to which said hydrogen stream from stage A) is supplied, and a gas-liquid washing section to which part of said ethanol stream from said stage E1) and a part of said stream are fed ethanol / acetaldehyde from said step A), and at least one ethanol enriched liquid stream and a purified hydrogen stream are obtained. It is preferred that no other streams be fed to said step C1).

The fraction of said ethanol / acetaldehyde stream leaving step A) is from 0 to 100%. Using a portion of said ethanol / acetaldehyde stream can reduce the consumption of a portion of said ethanol-rich stream from said step E1).

Stage C1) allows you to get a very clean stream of purified hydrogen, that is, containing at least 90 mol% of hydrogen, preferably 99 mol% of hydrogen, preferably 99.8 mol% of hydrogen. The purified hydrogen stream also contains traces of water and ethanol. This stage also allows you to extract ethanol and acetaldehyde contained in the hydrogen stream leaving the specified stage A), thus making it possible to return to the cycle and maximizing the total efficiency of the method.

The use of a portion of the ethanol-rich stream from step E1) and a portion of the ethanol / acetaldehyde stream from step A) instead of water, as was done in the prior art, can reduce the total flow of water circulating in the process. Thus, the total flow rate of water supplied at the stages E1) and E2) of the treatment of the effluent is reduced, which reduces the size of the equipment and the flow of energy at stages E1) and E2). In addition, as described above, the ethanol-rich liquid stream exiting from the indicated step C1) can be directly fed to the step B) of conversion to butadiene without treatment in the step E1) of the treatment of the effluent.

The authors of the application found that in the method according to the invention, ethanol is a much better solvent than water for washing acetaldehyde, which reduces the size of the equipment used in stage C1) according to the invention compared to the prior art.

The hydrogen stream leaving step A) is compressed in a compression section to a pressure in the range from 0.1 to 1.0 MPa, preferably from 0.1 to 0.7 MPa, more preferably from 0.4 to 0.68 MPa. The purpose of this compression is, on the one hand, to reduce the volumetric flow of gas, and on the other hand, to improve the efficiency of downstream washing.

The compressed hydrogen stream is then cooled to a temperature in the range from 25 ° C to 60 ° C, preferably from 30 ° C to 40 ° C, and then fed from below to the washing column of the washing section, where it is brought into contact with said part of the ethanol stream from the stage E1) and the indicated portion of the ethanol / acetaldehyde stream from step A), wherein said partial streams are supplied from above and at an intermediate point of said wash column, respectively. Before being fed into said wash column, each of these partial streams is cooled to a temperature in the range of from 15 ° C to -30 ° C, preferably from 0 ° C to -15 ° C. Preferably, the ethanol-enriched stream leaving step E1) is supplied at a temperature lower than the temperature of said portion of the ethanol / acetaldehyde stream from step A), thereby creating a temperature gradient between the top and bottom of the column and reducing solvent losses in the purified hydrogen stream. The gas-liquid washing column in the washing section is equipped with plates or random or structured nozzles.

The authors of the application found that the presence of a large amount of ethanol compared to water in the indicated washing section allows working at lower operating temperatures without the risk of hydrates in this column. The low temperature of the washing liquids and the temperature gradient between the top and bottom of the column allows a very good extraction of acetaldehyde present in the compressed hydrogen stream and very good purity of the purified hydrogen stream taken in the head of said washing section. Thus, the loss of acetaldehyde in the purified hydrogen stream is zero. In addition, the loss of ethanol in purified hydrogen is very low due to the low temperature of ethanol introduced into the head of the washing section, which is allowed due to the absence of hydrate formation.

Optional Step C2) Hydrogen Stream Finishing

Step C2) of the final hydrogen treatment is preferably carried out after step C1). Said step C2) comprises at least a gas-liquid washing section to which a purified hydrogen stream from step C1) is supplied and a pure water stream external to the process or a water-rich stream leaving step E1), and produces purified hydrogen flow and waste water flow.

The specified washing section contains at least one gas-liquid washing column, into which the specified purified hydrogen stream from step C1) is supplied from below, and the pure water stream or water-rich stream from step E1) is supplied from above, and which gives the purified hydrogen stream from above, and below the flow of waste water.

This step allows the extraction of the last traces of ethanol, possibly contained in the purified hydrogen stream from step C1). The specified stage C2), similar to the processing of hydrogen in accordance with the prior art, consumes, however, much less water than in the prior art, since the hydrogen stream supplied to stage C2) was previously treated in stage C1) and, thus thus freed of all acetaldehyde entrained in the hydrogen stream leaving from stage A). In addition, ceteris paribus, removing traces of ethanol by washing with water requires less expense than removing traces of acetaldehyde. In addition, since ethanol is less volatile than acetaldehyde, under the same operating conditions it is much less entrained in the hydrogen stream than acetaldehyde.

Stage D1) Butadiene Extraction

According to the invention, at least stage D1) of the extraction of butadiene containing at least one compression section, a gas-liquid washing section and a distillation section, at least said gaseous and liquid streams leaving from said stage B) are fed, an ethanol stream consisting of said ethanol feedstock and / or part of the ethanol stream exiting from step E1), and at least a gaseous by-product stream, a crude butadiene stream and an ethanol / acetaldehyde / water stream are obtained.

The specified ethanol stream fed to stage D1) preferably contains at least 80 wt.% Ethanol, preferably at least 90 wt.%, Preferably at least 93 wt.%. The specified ethanol stream supplied to stage D1) may contain methanol, water, ethyl acetate, butanol and hexanol. Preferably, said ethanol stream fed to step D1) contains less than 10 wt.% Acetaldehyde, preferably less than 5 wt.% And more preferably less than 1 wt.%. Preferably, said ethanol stream fed to step D1) contains less than 20 wt.% Water, preferably less than 5 wt.%, More preferably less than 1 wt.%.

In one preferred configuration, said ethanol stream fed to step D1) consists of said ethanol feedstock. An advantage of this configuration is that said feed does not contain reaction by-products that are formed in stages A) and B) and which can be concentrated due to recycling. In particular, this ethanol feed does not contain acetaldehyde at all or only in trace amounts.

In another preferred configuration, said ethanol stream consists of a portion of the ethanol stream exiting from E1) processing of the effluent.

The use of an ethanol stream containing little or no acetaldehyde free minimizes the entrainment of acetaldehyde into the specified stream of gaseous by-products taken from above the specified section of the gas-liquid washing, which reduces the loss of the total productivity of the process, and also reduces the flow rate of the washing water required at the stage F).

The gaseous stream exiting from stage B) is compressed in the specified compression section to a pressure in the range from 0.1 to 1.0 MPa, preferably from 0.1 to 0.7 MPa, preferably from 0.2 to 0.5 MPa. The purpose of this compression is, on the one hand, to reduce the volumetric flow rate of gas, and on the other hand to improve the efficiency of later washing. Preferably, the compressed gaseous stream is then cooled to a temperature in the range from 25 ° C to 60 ° C, preferably from 30 ° C to 40 ° C.

Preferably, said gas-liquid washing section in stage D1) comprises a washing column into which said ethanol stream supplied to stage D1 is fed from above, and a compressed and cooled gaseous stream from below and a gaseous by-product stream is obtained from above and a liquid stream from below. which is fed to said rectification section of step D1).

The specified ethanol stream supplied to stage D1) is cooled before being fed to the head of said gas-liquid washing column of the washing section at a temperature of from 20 ° C to -20 ° C, preferably from 15 ° C to 5 ° C. The benefit of cooling said ethanol stream is to improve the efficiency of the washing operation by reducing the entrainment of ethanol and acetaldehyde into said gaseous by-product stream. In this way, all butadiene present in the compressed and cooled gaseous stream leaving step B) is washed away, and the vaporous by-product stream taken from the top of said gas-liquid washing section does not contain butadiene.

Incidentally, minimizing the entrainment of acetaldehyde into the specified gaseous by-product stream can significantly reduce the water flow required in step F) of washing the gaseous by-products with water, the purpose of which is to extract ethanol and possible traces of acetaldehyde entrained in the gaseous by-product stream taken from the top of the washing section ethanol in stage D1).

Preferably, the butadiene enriched ethanol stream taken from the bottom of said gas-liquid washing section in step D1), as well as the liquid stream from step B), is supplied to said distillation section of step D1) in order to separate the steam stream containing most of the butadiene called a stream of crude butadiene, and the bottom residue is ethanol / acetaldehyde / water. The term "containing most" means that the stream contains more than 80% butadiene, preferably more than 90%, preferably more than 95%, more preferably 98%, very preferably more than 99% and very preferably all butadiene contained in the feed to the specified section distillation. The specified ethanol / acetaldehyde / water residue contains ethanol and acetaldehyde, and also contains the water obtained in stage B), and by-products formed in stages A) and B), such as diethyl ether and ethyl acetate, and brown oils. The residue ethanol / acetaldehyde / water is then fed to the effluent treatment step E2). The specified distillation section operates at a pressure in the range from 0.1 to 1 MPa, preferably from 0.2 to 0.5 MPa.

The scheme of recirculation and use of external streams proposed by the invention (ethanol feedstock, water), in particular, cooled ethanol stream, allows to minimize the flow rate of the spent water, as well as the stream for processing in the indicated sections E1 and E2). Thus, the method according to the invention allows to minimize the consumption of streams processed at the stage of processing the output streams.

Step D2) First Purification of Butadiene

Stage D2) of the first purification of butadiene comprises at least a gas-liquid washing section, to which a stream of crude butadiene from step D1) is supplied from below, and a stream of water, which may be a stream from a source external to said process for producing butadiene, from above, and / or a part of the water stream leaving step E1), wherein in the indicated washing section a pre-purified stream of butadiene is obtained from above and a stream of waste water from below. Preferably, said water stream is a stream of water from a source external to the process.

The specified waste water stream contains acetaldehyde and some butadiene and can be sent to the effluent treatment step E1), to the acetaldehyde distillation section, or to step E2).

The aim of stage D2) is to remove polar impurities, in particular acetaldehyde, the content of which in the final butadiene should not exceed several ppm. The crude butadiene stream leaving step D1) contains mainly butadiene but also contains many impurities, including a significant amount of acetaldehyde, which forms an azeotrope with butadiene and therefore cannot be completely removed by distillation in step D1). Thus, the flow rate of the specified water stream is set so as to achieve the desired specification for acetaldehyde in the pre-purified stream of butadiene.

Said water stream is cooled to a temperature below 25 ° C, preferably below 20 ° C, before being flushed to the gas-liquid washing section to flush with less water. The feed temperature of said water stream is selected so that hydrates do not form with butadiene and light hydrocarbons still present in the crude butadiene stream leaving step D1). The pressure in the wash column is determined so as to ensure the absence of condensation of butadiene so that it remains in the form of gas. The pressure at this stage is from 0.1 to 1 MPa, preferably from 0.2 to 0.3 MPa.

Optional step D2b) second purification of butadiene

The pre-purified butadiene stream exiting from step D2) is preferably subjected to step D2b) of a second purification of butadiene before being fed to step D3) of further purification of butadiene, said step D2b) containing at least a washing section to which said pre-purified butadiene stream is fed from below from stage D2), and on top of the absorbing solution. A pre-purified stream of butadiene is removed from the above washing section, from which traces of acetaldehyde still contained in the pre-purified stream of butadiene, as well as traces of other carbonyl compounds that are less soluble in water than acetaldehyde, such as butanal, acetone and hexanal, were removed , and therefore less efficiently removed by simple washing with water. A liquid stream is taken from the bottom of the indicated washing section, which is removed from the process.

In a first embodiment of said step D2b), said absorbent solution is an aqueous solution with a pH above 10 determined by adding sodium hydroxide or potassium hydroxide.

In a second embodiment of said step D2b), said absorbent solution is an aqueous solution of sodium or potassium bisulfite, the pH of which is from 5 to 8, preferably from 6 to 7.

In a third embodiment of said step D2b), said absorbent solution is an aqueous solution containing a compound from the hydrazine family.

The inventors have found that the combination of steps D2) and D2b) is particularly suitable for treating a crude butadiene stream obtained by the process for producing butadiene from ethanol.

Indeed, the implementation of only stage D2) requires high water consumption in order to achieve a specification for carbonyl compounds of less than 10 ppm. These large flows of water are then treated in step E1), which results in corresponding operating costs and capital costs. In addition, due to a very significant increase in the flow rate of water supplied to stage D2), a small fraction of butadiene dissolves, which reduces the overall performance of the process.

In addition, the implementation of only stage D2b) is not advisable for processing the stream of crude butadiene leaving stage D1). Indeed, acetaldehyde removed from the crude butadiene stream by contact with an aqueous solution of a base, or a solution of bisulfite, or an aqueous solution of a compound from the hydrazine family is difficult to regenerate. Therefore, a significant amount of acetaldehyde will be lost, which is reflected in a decrease in the total productivity of the process.

Thus, the authors of the application have established the optimal functioning of the method, coordinating the stages D2) and D2b) of the first and second purification of butadiene, which allows to achieve specifications, while increasing the total productivity of the process and minimizing operating costs.

Step D3) Further Purification of Butadiene

According to the invention, at least step D3) for further purification of butadiene is supplied with at least said pre-purified stream of butadiene exiting from said step D2), preferably processed in step D2b) of a second purification, and at least one purified stream of butadiene is obtained.

The specified stage D3) allows you to clean the butadiene obtained in the reaction stages, to a very high degree of purity (more than 99.5 wt.%, Preferably more than 99.8 wt.% And very preferably more than 99.9 wt.%) While limiting product losses when separating impurities that are not removed or only partially removed during stages D1), D2) and, preferably, D2b).

In a first embodiment of the invention, said step D3) comprises at least a drying section, a cryogenic distillation section and a butadiene / butene separation section by liquid-liquid extraction.

The pre-purified butadiene stream exiting from step D2), preferably treated in step D2b), is fed to the drying section. The aim of this section is to achieve the required water specifications in the final product (purified butadiene stream) and to allow cryogenic separation without risk of hydrate formation. At the outlet of said drying section, a stream of dry butadiene is obtained. Dry butadiene is understood to mean butadiene with a water content of less than 10 ppm, preferably less than 5 ppm, preferably less than 1 ppm.

The specified drying section preferably includes a dryer consisting of one or more tanks containing one or more adsorbents having a high affinity for water. This adsorbent may consist, without limitation, of silicon oxide and / or alumina. Said adsorbent can be, without limitation, a zeolite, such as zeolite 3A or 4A. When the adsorbent or adsorbents are saturated with water, said pre-purified stream of butadiene is supplied to another reservoir containing fresh or regenerated adsorbent or adsorbents.

The adsorbent can be regenerated either by changing the partial pressure of water in the tank, or by changing the temperature in the tank, or by simultaneously changing both. In the latter embodiment, the regeneration of the adsorbent or adsorbents saturated with water is carried out by heating the tank while supplying a stream containing no or very little water to it. By the absence or very low water content is meant a water content of less than 500 ppm, preferably less than 350 ppm, preferably less than 10 ppm, preferably less than 5 ppm, very preferably less than 1 ppm. This stream, containing no or little water, can be, without limitation, a nitrogen stream, an air stream, a hydrocarbon stream or a hydrogen stream. In one preferred embodiment of the invention, a portion of the purified hydrogen stream leaving step C1) is used.

Said stream, completely free or low in water, is heated to a temperature sufficient to regenerate the adsorbent or adsorbents, preferably to about 250 ° C., before being fed to the reservoir containing the adsorbent or adsorbents to be regenerated.

According to this first embodiment, said dry butadiene stream is then fed to a cryogenic distillation section using a distillation column. Light products exit the top of the cryogenic distillation section at a temperature of -25 ° C to -35 ° C. The cube of the column is at a temperature of from 20 ° C to 50 ° C, preferably from 25 ° C to 45 ° C, very preferably from 30 ° C to 40 ° C, the pressure in the head of the column is from 0.3 to 0.4 MPa, preferably 0.35 MPa. This column is advantageous in that it has a very high separation efficiency of the last non-condensable gases, without loss of butadiene (less than 0.05%). Thus, a significant return to stage D1) and loss of butadiene are avoided.

According to this first embodiment, the bottom product from said cryogenic distillation section, called the butadiene stream freed from light fractions, always contains butenes as the main impurity. The specified stream of butadiene freed from light fractions, served in the separation section of butadiene / butenes by liquid-liquid extraction, as described in patent FR 2036057.

Said butadiene / butene separation section is a liquid-liquid extraction section into which said butadiene stream, free from light fractions, is supplied to the intermediate zone of the first liquid-liquid extraction column, and into which a polar solvent stream, preferably DMSO, is fed from above. A solvent is provided below, which is a saturated hydrocarbon solvent, preferably pentane or cyclohexane. The costs, as well as the ratio of the costs of the polar solvent to the hydrocarbon solvent, are set so that the main part of butenes is entrained in the hydrocarbon solvent, and the main part of butadiene is entrained in the polar solvent.

The butene / hydrocarbon mixture obtained on top of the first extraction column is then treated in the first distillation column to obtain a butene stream from above and a hydrocarbon solvent that can be recycled from below.

A mixture of butadiene with a polar solvent is then fed to the head of the second liquid-liquid extraction column, in which the butadiene is extracted from the polar solvent, bringing it into direct contact with a larger amount of hydrocarbon solvent than in the first liquid-liquid extraction column, which is introduced from the bottom of the second column liquid-liquid extraction.

The butadiene / hydrocarbon mixture obtained in the head of the second liquid-liquid extraction column is then treated in a distillation column to obtain a purified butadiene stream from above and a hydrocarbon solvent that can be recycled from below.

Preferably, the liquid-liquid extraction columns in said butadiene / butene separation section operate at a pressure of from 0.1 to 1 MPa and a temperature of from 20 ° C to 60 ° C.

In another embodiment of the invention, said step D3) comprises at least one simple distillation and one extractive distillation. The simple distillation step may be carried out upstream or downstream of the extractive distillation step. Extractive distillation can be carried out, without limitation, with a solvent such as N-methylpyrrolidone, dimethylformamide or acetonitrile.

Of course, at various stages of the processing and purification of butadiene D1), D2), D2b) and D3), any stream containing butadiene that can be obtained in other processes located close to the process by the method according to the invention can also be processed simultaneously.

Step E1) Exit Processing

According to the invention, at least water / ethanol / acetaldehyde raffinate leaving step E2) is fed to the effluent treatment step E1), and at least an ethanol enriched stream, an acetaldehyde-rich stream and a water-rich stream are obtained. If the waste water stream leaving from stage D2), or the water-alcohol mixture stream leaving from stage F), or the stream of waste water leaving from stage C2) are not subjected to stage E2), removing impurities and brown oils, they can be fed directly to stage E1) processing the outgoing streams. A portion of the ethanol feed is also preferably fed to section E1).

Unlike the prior art, it is preferable not to carry out any screening with a loss of ethanol or acetaldehyde.

Preferably, said step E1) comprises at least two distillation sections: a water and ethanol distillation section and an acetaldehyde distillation section.

The specified water / ethanol / acetaldehyde stream exiting from step E2) and, optionally, the waste water stream exiting from step D2) are fed to said acetaldehyde distillation section, in which acetaldehyde is separated off to form an acetaldehyde enriched stream, and the remainder from the specified the distillation sections of acetaldehyde are fed to the distillation section of water and ethanol, which allows the ethanol enriched stream to be separated from above and the water enriched stream below. Since the water-alcohol mixture stream leaving step F) and the waste water stream leaving step C2) do not contain acetaldehyde, they can be fed directly to the said distillation section of water and ethanol.

The ethanol-rich stream exiting from step E1) consists predominantly of ethanol. The word "predominantly" means a content of more than 80 wt.%, Preferably more than 84 wt.%. The ethanol-rich stream leaving step E1) may contain impurities, such as, but not limited to, water, ethyl acetate, butanol, and hexanol.

Apart from water, the remaining impurities comprise less than 10%, preferably less than 5%, even more preferably less than 2% by weight of the stream.

The acetaldehyde-rich stream leaving step E1) consists mainly of acetaldehyde and ethanol. By "predominantly" is meant a content of more than 80% by weight, preferably more than 85% by weight. The acetaldehyde-rich stream leaving step E1) may contain impurities, such as, but not limited to, water, ethyl acetate, acetone. Apart from water, the remaining impurities comprise less than 10 wt.%, Preferably less than 5 wt.% Of the stream.

These streams, respectively enriched with acetaldehyde, ethanol and water, are then returned to the rest of the process according to the invention. The fraction of said ethanol-rich stream fed to step A) is preferably at least 0.7, preferably at least 0.75, very preferably at least 0.8. The proportion of said water-rich stream fed to said step F) is preferably from 0 to 0.3, very preferably from 0 to 0.1, more preferably from 0 to 0.01. The proportion of said water-rich stream fed to said step E2) of removing impurities and brown oils is preferably from 0 to 1, preferably from 0.3 to 0.6, and more preferably from 0.4 to 0.5.

In another embodiment of the invention, said streams, respectively enriched in acetaldehyde, ethanol and water, are subjected to a purification step before returning to the rest of the process. By purification is meant contacting said streams with adsorbents, such as, for example, activated carbon, silica, alumina or a functionalized polymer resin. For example, activated carbon removes traces of butanol and hexanol contained in a stream enriched in ethanol. For example, a base resin removes acetic acid present in a stream enriched in water. After the adsorbents are saturated and will no longer ensure the purity of the streams enriched with acetaldehyde, ethanol and water, respectively, they should either be removed or regenerated for reuse.

Stage E2) removal of liquid impurities and brown oils

According to the invention, at least ethanol / acetaldehyde / water stream leaving from stage D1) and a part of the water stream leaving stage E1) are fed to step E2) for removing impurities and brown oils, and at least ethanol / acetaldehyde / raffinate is obtained water, a stream of light brown oils, and a stream of heavy brown oils.

Preferably, said step E2) comprises at least a straight-through / counter-current washing section, a light brown oil distillation section and a heavy brown oil distillation section.

The ethanol / acetaldehyde / water stream from step D1) is preferably fed to said direct-flow / counter-flow washing section at an intermediate point, preferably in a mixture with a waste water stream leaving step D2), a water-alcohol mixture stream leaving step F), and a waste water stream leaving step C2) (if this last step is used), preferably in admixture with a part of the waste water stream leaving step D2). Since these streams contain more water than the ethanol / acetaldehyde / water stream leaving step D1), introducing them as a mixture can reduce the loss of hydrocarbon in the raffinate.

Preferably, a hydrocarbon stream is fed to the bottom of the straight-through / counter-current washing section, and a portion of the aqueous stream from step E1), which does not contain ethanol and acetaldehyde, is supplied from above. The hydrocarbon stream and part of the water stream from step E1) are supplied at a temperature of preferably from 10 ° C to 70 ° C, preferably from 45 ° C to 55 ° C. The said direct-flow / counter-current washing section gives the extracted extracted hydrocarbons on top containing part of the impurities and brown oils, and the indicated ethanol / acetaldehyde / water raffinate on the bottom.

The said forward / counterflow washing section preferably operates at a pressure of from 0.1 to 0.5 MPa, preferably from 0.2 to 0.4 MPa. Preferably, the addition of water for countercurrent washing is such that the water content in the raffinate water / ethanol / acetaldehyde is higher than 30 wt.%, Preferably higher than 40 wt.%.

In one embodiment, the contact between the two liquid phases in said direct-flow / counter-current washing section is carried out in a liquid-liquid extractor. Various contact options may be provided. You can name, without limitation, a packed column, a column with a pulsating flow, or a sectioned column with stirring. In another embodiment, the contact between the two liquid phases in said direct-flow / counter-current washing section is realized in a membrane contact device or in a cascade of membrane contact devices. This contact option is particularly suitable for the system used. Indeed, it is known that mixtures of water, ethanol and hydrocarbon form stable emulsions, which can lead to problems in the liquid-liquid extractor. The membrane contact device allows you to create a large contact area, which facilitates the transfer of impurities and oils to the hydrocarbon phase without the formation of an emulsion.

The specified extract of washing hydrocarbons is fed to the specified section of the distillation of light brown oils, which gives as a distillate the specified stream of light brown oils, as well as residual hydrocarbons containing part of the heavy brown oils.

The specified stream of light brown oils consists of impurities formed in reaction stage B), mainly from diethyl ether, ethyl acetate and crotonaldehyde, as well as from a light fraction of brown oils, consisting of impurities in lower amounts, among which are pentene, isoprene, butanal, vinyl ethyl ether. This stream can be burned to provide part of the heat needed for the hot oil circuit or for process steam boilers, or distilled to extract a diethyl ether stream and / or an ethyl acetate / crotonaldehyde stream, which can either be processed or returned to the reaction section of step B ) for re-transformation.

These residual hydrocarbons contain mainly hydrocarbons used for washing, as well as the heaviest brown oil fraction. In order to prevent the accumulation of brown oils as a result of the return of the hydrocarbon stream to the liquid-liquid extractor, a portion of these residual hydrocarbons is treated in the indicated heavy oil distillation section, which consists of a distillation column, which gives a hydrocarbon distillate, consisting mainly of hydrocarbons and also containing some traces of brown oils and, as a residue, said heavy brown oil stream containing more than 80%, preferably more than 85% hydrocarbons, and also most t yazy brown oils. The fraction of said hydrocarbon stream directed to said oil distillation section is from 5% to 30% of the total flow of said residual hydrocarbons, preferably from 10% to 20%. The hydrocarbon distillate is mixed with a portion of the residual hydrocarbons that have not been treated in said heavy oil distillation section to form a hydrocarbon stream supplied to said straight-through / counter-flow washing section.

This stream, which preferably comprises from 0.1% to 20% of the charge of said heavy oil distillation section, preferably from 0.3% to 5%, can be burned to provide part of the heat needed for the hot oil circuit or for process steam boilers. In order to maintain a constant flow for washing, the introduction of hydrocarbons is required, equivalent to the loss in the cube of the specified section distillation of heavy oils. This column is adjusted so as to maintain a constant concentration of brown oils in the hydrocarbon recirculation loop (hydrocarbon stream / wash hydrocarbon stream).

Streams of light and heavy brown oils are removed from the process.

The ethanol / acetaldehyde / water stream leaving step D1) contains mainly ethanol, acetaldehyde, water, as well as impurities such as diethyl ether, ethyl acetate, and brown oils, as defined above. If these impurities are returned to the reaction stages A) and B), they can accumulate in the distillate fraction rich in acetaldehyde and / or in the distillate fraction rich in ethanol, which only partially reacted in the reaction sections of stages A) and B). Stage E2) allows you to extract some of these impurities before stage E1) of the treatment of the effluent, which avoids the separation of brown oils in distillation columns, simplifies the distillation scheme and obtain an ethanol stream, acetaldehyde stream and a stream of water with a higher degree of purity than in the prior art.

The straight-through washing of the ethanol / acetaldehyde / water stream leaving from stage D1) with a hydrocarbon stream entrains some impurities, while the counter-current washing of the hydrocarbon stream entrains some of the impurities and brown oils along with a part of the water stream leaving from stage E1) to reduce acetaldehyde losses and ethanol.

The inventors unexpectedly found that liquid phase separation could be carried out by adding certain hydrocarbons to the ethanol / acetaldehyde residue leaving Step D1). This result is unexpected, since the ethanol / acetaldehyde residue leaving the stage has a very high content of ethanol and acetaldehyde, which are mixed with hydrocarbons in any proportions. The authors of the application found that, with the right choice of hydrocarbon, liquid-liquid phase separation can be achieved and, therefore, liquid-liquid extraction can be carried out in order to remove some of the impurities contained in the ethanol / acetaldehyde / water stream leaving stage D1). The specified hydrocarbon stream may contain saturated and / or unsaturated and / or aromatic hydrocarbons, preferably saturated hydrocarbons. The specified hydrocarbon stream preferably consists of a mixture of hydrocarbons containing from 6 to 40 carbon atoms, preferably from 10 to 20 carbon atoms. Said hydrocarbon stream may be, without limitation, a gas oil or desulfurized kerosene fraction or a hydrocarbon fraction obtained from a Fischer-Tropsch-type apparatus.

The addition of water to the direct-flow / counter-current washing section allows a better functioning of the process for removing impurities and brown oils according to the invention.

Thus, the method according to the invention avoids the regular release of ethanol in order to prevent the accumulation of brown oils, which improves the overall efficiency of the method.

Stage F) washing with water gaseous by-products

According to the invention, a gaseous by-product stream from step D1), as well as a portion of the water-rich stream from said step E1) are fed to water washing step F), and at least a stream of water-alcohol mixture is obtained.

The aim of said step F) is to recover a small portion of ethanol entrained in said gaseous by-product stream leaving step D1) in order to increase the overall process productivity.

According to the invention, the amount of water leaving the indicated step E1) required in the indicated step F) is very low, in contrast to the amount of water required according to the prior art, since the vapor stream from step B) was washed in ethanol in step D1) a stream containing little or no acetaldehyde. Therefore, a small fraction of ethanol remains in this stream, which is easy to extract with less water than the amount of water that would be required if traces of acetaldehyde were contained in the gaseous by-product stream from step D1).

The water filled with ethanol after washing is taken from the indicated stage F), it forms a stream of a water-alcohol mixture. It is preferably fed to step E1), directly to the distillation section of the water-ethanol mixture, without passing acetaldehyde through the distillation section. In another embodiment of the invention, it is preferably supplied to step E2) of removing impurities and brown oils.

Thus, the method according to the invention allows to minimize the flow rate of the processing at the stage of processing of the output streams. In addition, it allows to minimize the loss of butadiene, allowing you to extract more than 98%, preferably more than 99% of the butadiene obtained at the end of the reaction stages, in the specified purified stream of butadiene.

Description of figures

Figure 1 schematically and without limitation shows one configuration of the method according to the invention.

A portion of the ethanol stream leaving the distillation section 71 is sent via line 1 to reaction section 2, where a portion of the ethanol is converted mainly to acetaldehyde and hydrogen. The stream from this reaction section is sent along line 3 to separation section 4.

Separation section 4 allows you to separate the hydrogen stream 5, compressed in section 6, and the ethanol / acetaldehyde stream, which is divided into two parts, one of which is fed through line 52 to the reaction section 18, and the other is sent through line 50 to the washing section 8, so that rinse the compressed hydrogen stream 7. The compressed hydrogen stream is also washed with a portion of the ethanol stream 49 leaving the distillation section 71 and discharged as purified hydrogen stream through line 10. This block is described more specifically in FIG. 2.

The reaction section 18 is fed with an acetaldehyde stream from the distillation section 71 via line 17, an ethanol / acetaldehyde stream, which was used to wash the hydrogen, via line 51, and an ethanol / acetaldehyde stream, fed through line 52 from the separation section 4. Stream from the reaction section 18 is directed to a separation section 20 along line 19 to separate into a gaseous stream 21 and a liquid stream 31.

The gaseous stream 21 is compressed in section 22. It is fed through line 23 to the washing section 24, where it is washed by contact with ethanol feedstock 15. This block is more specifically described in FIG. 3. The compressed and washed gaseous stream is fed through line 26 to the water washing section. 27, where it is washed with a portion of the aqueous stream 53 leaving the distillation section 71. Water filled with ethanol after washing is returned via line 30 to the distillation section 71, directly to the water-ethanol separation column without passing acetaldehyde through the distillation column. The steam stream washed in section 27 is sampled on line 28.

The liquid stream leaving the separator 20 through line 31 is mixed with bottoms liquid from a flushing 24 coming through line 25. The mixture is sent to distillation 32, where the butadiene fraction will be separated and the mixture containing water, ethanol, acetaldehyde and impurities from below. The butadiene fraction is sent via line 33 to a water rinse 35, designed to remove polar impurities and especially acetaldehyde. Wash water, which is pure water, is introduced via line 36. Water filled with acetaldehyde is returned via line 37 to distillation section 71.

The pre-purified butadiene stream is sent via line 38 to the drying section 54 to remove all traces of water. The dry butadiene stream 56 is fed to a cryogenic distillation 57 and the water is taken off via line 55. This block is described in more detail in Figure 4. Light products exit the cryogenic distillation section at a temperature of -35 ° C along line 58, with a very low loss of butadiene. The butadiene fraction freed from light fractions exits line 59 and enters the liquid-liquid extraction section 60. The operation of this extraction section is described in more detail in FIG. 5.

The purified butadiene stream leaves the extraction section via line 62 with a purity sufficient for current specifications (more than 99.5%), the remaining impurities are mainly butenes. The butenes separated in this section (containing a small amount of butadiene) exit the unit via line 61.

The residual ethanol / acetaldehyde, which is a bottoms product of distillation 32, is sent via line 34 to a direct-flow / counter-current washing section of heavy hydrocarbons supplied through line 69, and reused water is supplied through line 64. Wash heavy hydrocarbons filled with impurities are discharged through line 65 and fed to the regeneration section 66, from which the heavy hydrocarbons 69 returned to the washing, the light fraction 67, containing, in particular, diethyl ether and ethyl acetate plus some light brown oils. The heavy fraction 68 containing heavy brown oils and a small portion of the washing hydrocarbons is also removed. The operation of sections 63 and 66 is described in more detail in figure 6.

The liquid from the cube of the direct-flow / counter-current washing section 63, containing simultaneously the ethanol / acetaldehyde 34 residue, after eliminating these impurities having a high affinity for heavy hydrocarbons 69, and the washing water 64 are sent via line 70 to the distillation section 71. This section allows you to separate the acetaldehyde fraction returned through line 17 to the reaction section 18, the ethanol fraction partially returned to the reaction section 2 through line 1 and partially to flushing 8 through line 49, and the water fraction containing a little acetic acid, partially returned taken to flushing 27 on line 53 and flushing 63 on line 64, and the rest of the water is cleaned outside the installation on line 72. The operation of this section is described in detail in figure 7.

Figure 2 schematically and without limitation shows the separation of the stream from the reaction section 2 and the stage of the treatment of hydrogen.

The stream from the reaction section 2 is fed through line 3 to a tank 401, which allows the hydrogen stream 5 and the liquid phase 402 to be separated. The hydrogen stream 5 is compressed in a compressor 601. Then, the compressed hydrogen stream is sent via line 602 to a heat exchanger 603, which cools the gas using refrigerant 604 The compressed hydrogen stream exits the heat exchanger 603 via line 7 and enters from below into the adiabatic wash column 805, where it is washed with two liquids cooled to a low temperature.

The liquid phase 402 is pumped to a higher pressure by the pump 403 to form an ethanol / acetaldehyde stream 404. A portion 50 of the ethanol / acetaldehyde stream is cooled in a heat exchanger 806 using a refrigerant 807, which may be, for example, propane. The fluid exits the heat exchanger 806 via line 808 before entering the column 805 at an intermediate level between the top and bottom of the column.

A part of the ethanol stream leaving the distillation section 71 is delivered via line 49 to a first heat exchanger 801, which allows cooling the ethanol 49 and again heating the hydrogen leaving column 805 via line 809. At the outlet of this heat exchanger, the purified and heated hydrogen stream is removed from the process by line 10, and the cooled ethanol is sent via line 802 to the heat exchanger 803 for additional cooling using a refrigerant 810, which may be, for example, propane. Ethanol is sent via line 804 to column 805. A liquid stream from the bottom of column 805 is sent via line 51 to reaction section 18 mixed with ethanol / acetaldehyde 404 portion 52.

Figure 3 schematically and without limitation shows the separation of the stream from the reaction section 18 and part of the processing stage of the butadiene stream.

Stream 19 from reaction section 18 is fed to a separator 2001, in which the butadiene stream 21 and the liquid phase 2002 are separated. The butadiene stream 21 is compressed in compressor 2202, and the compressed vapor stream 2203 is then cooled in heat exchanger 2204 using refrigerant 2205.

The compressed and cooled vapor stream 23 is supplied to an adiabatic wash column 2404, where it will be washed with ethanol feed 15, previously cooled in the heat exchanger 2401 with refrigerant coming through line 2402. The pre-cooled ethanol feed goes through line 2403 to column 2404. Compressed and recovered from the top of the column washed steam stream 26, and bottom bottoms washing liquid 25.

The bottoms wash liquid 25 is mixed with the liquid phase 2002, which was previously pumped by pump 2003 and flows through line 31. The mixture of liquids 25 and 31 contains all the butadiene produced, it is sent to section 32.

Figure 4 schematically and without limitation shows the drying of butadiene on a sieve.

The pre-purified butadiene stream enters through line 38 for drying, it passes through an open valve 5402-1 or 2, then through a drying sieve contained in a tank 5403-1 or 2. Dry butadiene leaves the tank 5403-1 or 2 through an open valve 5404 -1 or 2, then along line 5405-1 or 2, and finally sent to cryogenic distillation along line 56.

The hydrogen stream enters through line 10, is heated in the heat exchanger 5406 by heat exchange with a heat carrier 5407, which may be, for example, hot oil.

At the outlet of the heat exchanger 5406, the hot hydrogen stream is sent via line 5407-2 or 5407-1 to the open valve 5408-2 or -1, and from there to the regeneration tank 5403-2 or -1. At the outlet of the tank 5403-2 or -1, hot gas filled with water passes through an open valve 5409-2 or -1, then through line 5410-2 or -1, line 5411 and then to heat exchanger 5412, where it is cooled, and water is condensed by means of cooling water flowing through line 5413. Gas can also be cooled with an air cooler. The cooled gas leaving the heat exchanger 5412 is sent via line 5414 to a separator 5415 where condensed water is separated and removed from the unit via line 55. The condensed water contains part of the ethanol contained in stream 10; it can optionally be sent to section 71 to recover ethanol .

Figure 5 schematically and without limitation shows the purification of butadiene with a polar solvent, for example, dimethyl sulfoxide (DMSO).

The dry butadiene stream is fed via line 59 to a first extraction column 6001, into which a polar solvent stream, which may be, for example, DMSO, flows from above via line 6002. A hydrocarbon solvent such as pentane or cyclohexane is fed from below to the column through line 6003.

A polar solvent and dissolved butadiene come out from the bottom of the column 6001 via line 6004, which are pumped by a pump 6005 and sent to the head of the column 6007 via line 6006. A larger amount of hydrocarbon solvent is introduced into the cube of the column 6007 via line 6049 to remove the butadiene from the polar solvent. A polar solvent freed from butadiene leaves the bottom of column 6007 through line 6008 and is pumped by pump 6009, and then returns to column 6001 through line 6002.

At the top of the column, butadiene dissolved in hydrocarbons is sent via line 6030 to a heat exchanger 6031, where it is heated by indirect heat exchange with the cube of column 6033. At the outlet of the heat exchanger 6031, the butadiene-solvent mixture is fed to column 6033 via line 6032.

Column 6033 is equipped with a device 6042, allowing to heat and boil the cube of the column using a coolant 6043, which may be, for example, low pressure steam. The steam leaving the top of the column through line 6034 is cooled and completely condensed in a heat exchanger 6035 using refrigerant 6036. At the outlet of the heat exchanger 6035, the condensed liquid is poured into the tank 6038 via line 6037. Then, the liquid is sent via line 6039 to the pump 6040. Part of the liquid is sent to as reflux to column 6033 along line 6041, and the remainder of the purified butadiene stream is withdrawn from the process through line 62.

The bottoms product from the column 6033, which is a hydrocarbon solvent, is sent via line 6044 to the pump 6045. After passing through the pump 6045, the solvent is sent via line 6046 to the heat exchanger 6031, where it is cooled as a result of indirect heat exchange with the raw material for the column 6033. After exiting the heat exchanger 6031, solvent is sent via line 6047 to heat exchanger 6048 to complete cooling with 6049 refrigerant. After leaving heat exchanger 6048, solvent is returned to scrub column 6007 via line 6049.

A mixture of a hydrocarbon solvent and butenes, with a slight loss of butadiene, comes out on top of column 6001. This mixture is sent to a heat exchanger 6011, where it is heated as a result of indirect heat exchange with a cube of column 6013. At the outlet of a heat exchanger 6011, a butene-solvent mixture is supplied to column 6013 along line 6012. Column 6013 is equipped with a device 6022 that allows heating and boiling of the cube of the column using coolant 6023, which may be, for example, low pressure steam. The steam leaving the top of the column through line 6014 is cooled and completely condensed in the heat exchanger 6015 using refrigerant 6016. After exiting the heat exchanger 6015, the partially condensed mixture is fed into the tank 6018 via line 6017. In this tank 6018, gas and liquid phases are separated. The liquid phase from the tank is sent via line 6019 to a pump 6020, and then directed as a return flow to column 6013 via line 6021. The vapor phase, consisting mainly of butenes and a small amount of butadiene, is withdrawn from the process via line 61, for example, to use like fuel.

The bottoms stream from the column 6013, which is a hydrocarbon solvent, is sent via line 6024 to the pump 6025. After passing through pump 6025, the solvent is directed through line 6026 to heat exchanger 6011, where it is cooled as a result of indirect heat exchange with loading of column 6013. After exiting heat exchanger 6011 the solvent is sent via line 6027 to the heat exchanger 6028 to complete cooling with the refrigerant 6029. After leaving the heat exchanger 6028, the solvent is sent to the wash column 6001 via line 6003.

Figure 6 schematically and without limitation shows the extraction of low-polar impurities and brown oils by direct-flow / counter-current washing.

The remainder of the ethanol / acetaldehyde 34 mixture is fed to the wash column 6301. A heavy hydrocarbon solvent (which may be, for example, a gas oil fraction or desulfurized kerosene or a fraction obtained from a Fischer-Tropsch plant) is fed to the bottom of the 6301 column through line 69, and part water stream 64 is fed to the head of column 6301.

A heavy hydrocarbon flush stream is taken from the top of column 6301 via line 65 and sent to section 66 for regeneration. It is again heated in heat exchanger 6601 by heat exchange with the cube of column 6603. After exiting heat exchanger 6601, a preheated stream of heavy washing hydrocarbons is sent via line 6602 to column 6603.

Column 6603 is equipped with a device 6612, allowing to heat and boil the cube of the column using a heat carrier 6613, which may be, for example, hot oil. The steam leaving the top of the column through line 6604 is cooled and completely condensed in a heat exchanger 6605 using refrigerant 6606. After leaving the heat exchanger 6605, the condensed liquid is poured into the tank 6608 via line 6607. Then, the liquid is sent via line 6609 to pump 6610. Part of the liquid is sent to as the return flow to the column 6603 on line 6611, and the rest is removed from the installation on line 67.

The bottoms fraction from column 6603 is sent via line 6614 to pump 6615. Part of the liquid exiting pump 6615 is sent via line 6618 to another distillation column 6619. The remainder is sent via line 6616 to heat exchanger 6601, which allows cooling the bottoms liquid 6616 by indirect heat exchange with raw materials 65 for the column 6603. The cooled bottoms liquid leaves the heat exchanger 6601 through line 6617 to be sent to the heat exchanger 6637.

The treatment column 6619 is equipped with a device 6630, allowing to heat and boil the cube of the column using a heat carrier 6631, which may be, for example, hot oil. The steam leaving the top of the column through line 6620 is cooled and completely condensed in a heat exchanger 6621 using refrigerant 6622. After exiting the heat exchanger 6621, the condensed liquid is poured into the tank 6624 via line 6623. Then, the liquid is sent via line 6625 to pump 6626. Part of the liquid is sent to as a return stream to column 6619 via line 6628, and the rest is sent via line 6629 to heat exchanger 6637 mixed with bottoms from column 6603, where it is cooled with 6638 refrigerant. Outgoing hydrocarbons 6637 return n about line 69 to the wash column 6301.

The overhead from column 6619 consists mainly of heavy hydrocarbons with some traces of black oil. In order to maintain a constant flow rate of the flushing fluid, equivalent application of heavy hydrocarbons (not shown) is necessary.

The bottoms liquid from the column 6619 leaves line 6631 and is pumped by pump 6632, and then sent via line 6633 to the heat exchanger 6634, where it is cooled by refrigerant 6635 and removed from the process via line 68. It can then be used, for example, as fuel. The refrigerant 6635 may be cooling water, you can also use air with an air cooler, or use the stream from the unit, which must be heated again, as refrigerant 6635.

Figure 7 shows one possible configuration of the distillation section 71.

The mixture of ethanol / acetaldehyde / water / polar impurities leaving the washing 63 is fed through line 70 to the distillation section 71. This stream is mixed with washing water filled with acetaldehyde coming through line 37 from the washing section 35. The mixture of these two streams is heated in a heat exchanger 7101 by indirect heat exchange with a stream 7133. The stream leaving this heat exchanger is supplied to the column 7103 via line 7102. The overhead from the column leaving the line 7104 completely condenses in the heat exchanger 7105 as a result of heat exchange with the refrigerant 7106. Flow, outlet The box from heat exchanger 7105 enters through reflux vessel 7108 through line 7107. Liquid from this vessel exits through line 7109 to pump 7110, which directs return flow to column 7103 via line 7111 and distillate (acetaldehyde rich stream) through line 17 to the reaction section 18. This distillate contains mainly acetaldehyde, as well as water, ethanol and other light impurities (diethyl ether, butanal, acetone, ethyl acetate, etc.).

Boiling in column 7103 is carried out using a heat exchanger 7112, for example, with low-pressure steam coming through line 7113. The bottoms product from column 7103, containing mainly water, ethanol, a little butanol, acetic acid and several other impurities, leaves line 7114, then it is directed by pump 7115 through line 7116 to column 7118. The washing water from the washing section 27, filled with ethanol, enters through line 30 and is mixed with bottoms product 7103 from line 7116. The mixture is sent via line 7117 to column 7118.

The overhead from column 7118 leaves line 7119, then is completely condensed in heat exchanger 7120 using refrigerant 7121. The stream leaving heat exchanger 7120 is fed through line 7122 to the return flow collector 7123. The liquid from this collector leaves line 7124 to pump 7125, which directs the return flow to column 7118 through line 7126, and distillate through line 7127, one part to reaction section 2 along line 1, and the other part to flushing 8 along line 49 (flow enriched with ethanol). By adjusting the ratio between these two settings, it is possible to establish the ethanol / acetaldehyde ratio at the reactor inlet of section 18. This distillate contains mainly ethanol, as well as water, some butanol and several other impurities.

Boiling in column 7118 is carried out using a heat exchanger 7128, for example, with low-pressure steam coming through line 7129. The bottoms product from column 7118 (stream enriched with water), containing mainly water and a little acetic acid, leaves line 7130 and is sent by pump 7131 through line 7132 to heat exchanger 7101, where it is cooled by indirect heat exchange with feed for column 7103. The product exits heat exchanger 7101 through line 7133 and is cooled in heat exchanger 7134 with refrigerant 7135. After leaving the heat exchanger, some water, for example vlyayut via line 64 to washing 63 and via line 53 to washing 27 and the remainder withdrawn through line 72 out of the installation.

Examples

The following examples are based on the performed simulation, taking into account the recirculation of flows and supplemented by thermodynamic data verified at experimental points (data on the equilibrium of the binary liquid-vapor system and the liquid-liquid distribution coefficient). In each example, the consumption of raw materials is selected so as to obtain an annual productivity of 150 · 10 ³ t / year of butadiene with a purity of 99.5-100 wt.% (In accordance with the actual use of the product), with an annual duration of the process of 8000 hours

Example 1 - A method of producing butadiene according to the prior art

1.1 - Hydrogen Treatment Step

The gas phase at the outlet of the reactor converting ethanol to acetaldehyde having a throughput of 10 t / h, contains hydrogen, also formed in the reaction, ethanol and acetaldehyde. It is important to limit the loss of ethanol and acetaldehyde to the maximum in order to maximize the overall performance of the process. Washing the gas phase with water allows you to remove 95.5 wt.% Acetaldehyde and ethanol contained in this gas phase.

The indicated washing goal is achieved using 50 t / h of water. These 50 tons of water can only be pure water, from a source external to the process, or partially consist of recycled water from the process. The loss of ethanol in the purified hydrogen stream is 31 kg / h.

The use of recycled water reduces the consumption of pure water, but as a result of recycling, acetic acid will be diverted into the purified hydrogen stream. A maximum of 40 t / h of circulating water can be used. Thus, the consumption of clean water will be at least 10 t / h. These 10-50 t / h of water make up only 35-70% of the flow of water processed in the entire technological scheme according to the prior art.

Regardless of whether the wash water is partially circulating water or completely pure water, the flow rate of water entering the distillation section of the water / ethanol / acetaldehyde mixture rises to 142 t / h.

1.2 - Stage of the first separation of butadiene, option 1

The vapor stream from the step of converting to butadiene is compressed, then washed, bringing into contact with a stream of ethanol / acetaldehyde pre-cooled to 35 ° C. leaving the reactor for converting ethanol to acetaldehyde. Rinsing said vapor stream with said ethanol / acetaldehyde stream allows almost all butadiene (99.988%) contained in said vapor stream to be recovered before washing. The steam stream leaving the washing forms a washed gas stream. It contains reaction by-products (ethylene, ethane, etc.), as well as ethanol and acetaldehyde.

The washed gas stream is then washed with recycled water to recover acetaldehyde and ethanol. It is necessary to use 12.7 t / h of water to extract all acetaldehyde and ethanol.

1.3 - Stage of the first separation of butadiene, option 2

This example differs from the previous example in that the ethanol / acetaldehyde stream leaving the ethanol to acetaldehyde conversion reactor is pre-cooled to 14 ° C. before being used to wash the pre-compressed steam stream from the butadiene conversion step.

Lowering the temperature of the ethanol / acetaldehyde stream allows all butadiene contained in said steam stream to be recovered and the amount of ethanol and acetaldehyde entrained in the washed gas stream is reduced.

The washed gas stream is then washed with recycled water to recover acetaldehyde and ethanol. 8.5 t / h of water must be used to recover all acetaldehyde and ethanol.

Example 2 - A method for producing butadiene according to the invention

2.1 - Stage of hydrogen treatment

The gas phase at the outlet of the reactor for converting ethanol to acetaldehyde is washed, after compression, with a part of the ethanol stream leaving the stage of processing the effluent. The washed gas phase forms a purified hydrogen stream. The loss of ethanol in the purified hydrogen stream is 32 kg / h, which is close to the loss of acetaldehyde 31 kg / h in the scheme according to the prior art.

Rinsing with return ethanol instead of water can reduce the flow rate of water introduced into the distillation section of the water / ethanol / acetaldehyde mixture by 50 t / h, i.e., reduce it to 91 t / h. This gives a gain of 35% compared with the flow rate of water circulating throughout the entire technological scheme, and, in particular, in the columns of the distillation section. This gain is expressed in lower investment and energy consumption throughout the ethanol and acetaldehyde recovery section.

2.2 - Stage of the first separation of butadiene, option 1

In this example, the steam stream from the step of converting to butadiene is compressed, then washed, bringing into contact with ethanol, which is the feedstock for the conversion process. The gas stream leaving the washing forms a washed gas stream.

The specified ethanol feed has the following composition: 93.3 wt.% Ethanol and 6.7% water, without measurable traces of impurities. It is fed to the wash column at a temperature of 35 ° C. This washing allows the recovery of 99.88% of the butadiene contained in said steam stream. The washed gas stream does not contain acetaldehyde, unlike the examples according to the prior art.

The washed gas stream is then washed with circulating water to recover ethanol. It is necessary to use 3.2 t / h of water to extract all ethanol, that is, much less than in the examples according to the prior art.

2.3 - Stage of the first separation of butadiene, option 2

This example differs from the previous one in that the ethanol feed is pre-cooled to 14 ° C before being used to flush the pre-compressed steam stream from the butadiene conversion step. This flushing allows you to extract all the butadiene contained in the specified steam stream.

The washed acetaldehyde-free gas stream is then washed with circulating water to recover ethanol. It is necessary to use 0.4 t / h of water to extract all ethanol, that is, more than 20 times less than according to the prior art.

Reducing the flow rate of water required for flushing, can reduce by 13% the flow rate of water at the entrance to the stage of processing of the effluent, thereby reducing the size of the separation equipment and its energy consumption.

This preferred embodiment of the invention, due to the use of ethanol feed compared with the use of a portion of the ethanol stream leaving the processing stage of the effluent, which reduces the flow rate for washing the butadiene fraction. Thus, the indicated ethanol consumption is reduced to 16%.

2.4 - Stage of the first separation of butadiene, option 3

In this example, the vapor stream from the butadiene conversion step is compressed, then washed, bringing into contact with a portion of the ethanol stream leaving the exit stream processing step. The gas stream leaving the washing forms a washed gas stream.

The specified ethanol stream leaving the stage of processing the effluent has the following composition: 84 wt.% Ethanol and 16 wt.% Water, without measurable traces of impurities. It is fed to the wash column at a temperature of 35 ° C. This flushing allows you to extract all the butadiene contained in the specified steam stream. The washed gas stream does not contain acetaldehyde, unlike the examples according to the prior art.

The washed gas stream is then washed with circulating water to recover ethanol. It is necessary to use 2.8 t / h of water to extract all ethanol, that is, much less than in the examples according to the prior art.

2.5 - Stage of the first separation of butadiene, option 4

This example differs from the previous one in that part of the ethanol stream exiting from the effluent treatment stage is pre-cooled to 14 ° C. before being used to rinse the pre-compressed steam stream from the butadiene conversion step. This flushing allows you to extract all the butadiene contained in the specified steam stream.

The washed acetaldehyde-free gas stream is then washed with circulating water to recover ethanol. It is necessary to use 0.4 t / h of water to extract all ethanol, that is, more than 20 times less than according to the prior art.

Reducing the flow rate of water required for flushing, can reduce by 13% the flow rate of water at the inlet of the processing stage of the effluent, thereby reducing the size of the separation equipment and its energy consumption.

2.6 - Stage additional separation of butadiene

The purified butadiene stream leaving the first purification of butadiene is fed to the drying section, sequentially through alumina, then through zeolite 4A, to remove all water possibly present in said purified butadiene stream. The stream leaving the drying section is a stream of dry butadiene. This dry butadiene stream is then fed to a cryogenic distillation column operating at a head pressure of 0.35 MPa, a cube temperature of 34 ° C and a head temperature of -33 ° C.

Finally, a distillation residue, called a butadiene stream free of light fractions, is fed to a liquid-liquid extraction section using DMSO and cyclohexane.

In the first wash column, 260 t / h of DMSO are fed from above and 52 t / h of cyclohexane from below. This first column contains 20 theoretical washing stages. The bottoms product from the first column is sent to the second wash column containing 10 theoretical stages.

The top product from this second wash column is treated in a distillation column, which allows the separation of butadiene from cyclohexane, and the column contains 24 theoretical stages and operates at a reflux ratio of 8.

The top product from the first wash column is treated in a distillation column, which allows you to separate butenes from cyclohexane, and the column contains 26 theoretical stages and works with a reflux ratio of 10.

99.3% of the butadiene entering the second separation step of butadiene is isolated as a product with a purity of 99.88% by weight.

At the outlet of the liquid-liquid extraction section, a purified butadiene stream is obtained with a butadiene content of 99.88% by weight. The loss of butadiene at all stages of purification (calculated as the ratio of the consumption of pure butadiene contained in the purified butadiene stream to the consumption of pure butadiene contained in the stream from the butadiene conversion reactor) is less than 0.8 wt.%.

The inventive stage and recirculation scheme, in particular, preventing the accumulation of impurities, makes it possible to return almost all unreacted compounds to the cycle. Thus, despite the fact that the degree of conversion in one pass through the reactor is low and comparable to that obtained according to the prior art, the total yield of butadiene obtained (in tons) per ton of ethanol converted is 41%. The use of the recirculation according to the invention allows to improve the overall productivity by more than 20 points in comparison with the scheme without recirculation, as well as to extract and process all the acetaldehyde present in the stream from the second stage of conversion. Thus, more than 99.9% of the ethanol contained in the process feed is processed.

Claims (24)

1. The method of producing butadiene from ethanol raw materials containing at least 80 wt.% Ethanol, including at least: A) a step for converting ethanol to acetaldehyde containing at least one reaction section, to which at least a portion of the ethanol-enriched stream leaving step E1) is supplied, operating at a pressure of 0.1 to 1.0 MPa and a temperature of 200 ° C to 500 ° C in the presence of a catalyst, and a separation section, allowing to separate the stream leaving the specified reaction section, at least a stream of hydrogen in gaseous form and a stream of ethanol / acetaldehyde in liquid form; B) a step for converting to butadiene containing at least one reaction section to which at least a portion of said ethanol / acetaldehyde stream leaving step A) is fed, a liquid stream enriched in ethanol leaving step C1), a portion of the stream enriched acetaldehyde leaving step E1), and wherein said section operates in the presence of a catalyst at a temperature of from 300 ° C to 400 ° C and a pressure of from 0.1 to 1.0 MPa, the feed rates being controlled so that the ethanol / mol ratio acetaldehyde at the entrance to the decree the reaction section involved was from 1 to 5; and also contains a separation section that allows you to split the stream leaving the specified reaction section into at least one gaseous stream and at least one liquid stream; C1) a hydrogen treatment step comprising at least a compression section compressing said hydrogen stream leaving step A) to a pressure of from 0.1 to 1.0 MPa, and a gas-liquid washing section, to which it is supplied at a temperature of from 15 ° C to -30 ° C a portion of said ethanol stream from step E1) and a portion of said ethanol / acetaldehyde stream from step A), and also said compressed hydrogen stream is fed at a temperature of 25 ° C to 60 ° C, and at least one ethanol-enriched liquid stream and a purified hydrogen stream; D1) a butadiene extraction step comprising at least a compression section compressing said gaseous stream exiting from step B) to a pressure in the range of 0.1 to 1.0 MPa, a gas-liquid washing section containing a washing column onto which an ethanol stream consisting of the indicated ethanol feedstock and / or a part of the ethanol stream exiting from step E1) is supplied from above at a temperature of 20 ° C to -20 ° C, and said gaseous stream exiting from step B) and cooled , and a distillation section operating at from 0.1 to 1 MPa, to which at least a liquid stream is supplied from the indicated stage B) and a liquid stream from the indicated gas-liquid washing section, wherein at the indicated stage D1) at least a gaseous by-product stream is obtained, the crude stream butadiene and ethanol / acetaldehyde / water stream; D2) a first butadiene purification step comprising at least a gas-liquid washing section to which a crude butadiene stream exiting from step D1) is supplied from below and a water stream, which may be a water stream external to the butadiene production process, from above , and / or a part of the water stream leaving stage E1), wherein in the indicated washing section a pre-purified stream of butadiene is obtained from above, and a stream of spent water from below; D3) a step for further purification of butadiene to which at least said previously purified butadiene stream exiting from said step D2) is fed, and at least a purified butadiene stream is obtained; E1) an effluent treatment step to which at least water / ethanol / acetaldehyde raffinate exiting from step E2) is fed, and at least an ethanol enriched stream, an acetaldehyde enriched stream, and a water enriched stream are obtained; E2) a step for removing impurities and brown oils, to which at least an ethanol / acetaldehyde / water stream exiting from stage D1) is supplied, and a water-enriched stream exiting from E1), and at least water / ethanol / acetaldehyde raffinate is obtained a stream of light brown oils and a stream of heavy brown oils; F) a water washing step to which a gaseous by-product stream leaving step D1) is supplied, as well as a portion of the water enriched stream leaving from said step E1), and in which at least one water-alcohol mixture stream is obtained. 2. The method of claim 1, wherein step C2) of the final hydrogen treatment is carried out after step C1), said step C2) comprising at least a gas-liquid washing section to which a purified hydrogen stream from step C1) and a clean stream are supplied water from a source external to the process, or a water-rich stream of water exiting from step E1), and a purified hydrogen stream and a waste water stream are obtained. 3. The method according to one of paragraphs. 1 or 2, wherein the pre-purified butadiene stream exiting from step D2) is subjected to step D2b) of a second purification of butadiene before being fed to step D3) of further purification of butadiene, said step D2b) containing at least a washing section to which a bottom is fed said previously purified butadiene stream from step D2), and an absorption solution is supplied from above. 4. The method according to claim 3, wherein said absorbing solution is an aqueous solution with a pH above 10, established by adding sodium hydroxide or potassium hydroxide. 5. The method according to claim 3, wherein said absorbing solution is an aqueous solution of sodium or potassium bisulfite, the pH of which is from 5 to 8. 6. The method of claim 3, wherein said absorbent solution is an aqueous solution containing a compound from the hydrazine family. 7. The method according to one of paragraphs. 1-6, in which step E2) comprises at least a straight-through / counter-current washing section, a light brown oil distillation section, and a heavy brown oil distillation section, wherein said ethanol / acetaldehyde / water stream is supplied at the intermediate point to said direct-flow / counter-current washing section leaving Step D1), a hydrocarbon stream is supplied from below, and a portion of the water enriched stream leaving from Step E1) is supplied from above, wherein said coal wash extract is fed to said brown oil distillation section odorants and receive as a distillate the specified stream of light brown oils and residual hydrocarbons, a portion of 5-30% of the total stream of these residual hydrocarbons is fed to the specified section for distillation of heavy oils, and a hydrocarbon distillate is obtained and, as a residue, the specified stream of heavy brown oils, wherein said hydrocarbon distillate and an untreated portion of said residual hydrocarbons are mixed to form a hydrocarbon stream supplied to said straight-through / anti-hydrocarbon section otochnoy washing. 8. The method according to one of paragraphs. 1-7, in which at least part of said ethanol feed is also supplied to said step A). 9. The method according to one of paragraphs. 1-8, in which the ethanol-enriched stream from step E1) is also supplied to said reaction section of said step B). 10. The method according to one of paragraphs. 1-9, in which the external reaction stream of acetaldehyde is also fed to said reaction section of said step B). 11. The method according to one of paragraphs. 1-10, in which no other streams are supplied to said step C1). 12. The method according to one of paragraphs. 1-11, in which the ethanol-enriched stream exiting from step E1) is supplied to said gas-liquid washing section of said step C1) at a temperature lower than the temperature of said portion of the ethanol / acetaldehyde stream from step A). 13. The method according to one of paragraphs. 1-12, wherein said step D3) includes at least a drying section, a cryogenic distillation section and a butadiene / butene separation section by liquid-liquid extraction. 14. The method according to one of paragraphs. 1-13, wherein said step D3) comprises at least one simple distillation and at least one extractive distillation. 15. The method according to one of paragraphs. 1-14, wherein a portion of said ethanol feed is also supplied to said section E1).

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